The present invention relates to elemental analyzers and analytical methods, particularly an analyzer employing a variable volume ballast chamber and its use for the collection of analytes and their subsequent analysis.
The determination of elements, such as carbon, hydrogen, and nitrogen, in an organic material is desirable for numerous reasons. Elemental analyzers, such as a CHN 2000 which is commercially available from Leco Corporation of St. Joseph, Michigan, have been used for a variety of applications. In recent years, the food market has become interested in determining the amount of protein in a sample which can be determined by the nitrogen content. Thus, the determination of nitrogen is important in providing such useful information to the nutritional market. The carbon-to-hydrogen ratio is desirable in the characterization of coal and coke samples, as is the carbon, hydrogen, and nitrogen ratios in a variety of other organic materials. Thus, elemental analyzers have been in use for these and other applications for some time.
Generally, the analysis of elemental carbon hydrogen and nitrogen is well known and is discussed in several references, including Methods in Microanalysis, Vol. 1, Mirra Osipovna Korshun, 1964, Instrumental Organic Elemental Analysis, R. Belcher, 1977; and Organic Elemental Analysis Ultramicro, Micro, and Trace Methods, Wolfgang J. Kirsten, 1983. U.S. Pat. No. 4,525,328 discloses an analyzer employing a fixed volume ballast chamber, which collects analytes in an approximately 4.5 L chamber for subsequent analysis. Such a system eliminates the rapid fouling of the various reducing agents and absorbing agents used in the system by the collection of a sample in the chamber and subsequent detection of an aliquot of the collected sample. The amount of combustion oxygen used in filling the fixed ballast chamber is significant, and an analysis takes a significant amount of time for the combustion and ballast chamber filling. Also, the byproducts of combustion, i.e., the analyte gases, are somewhat diluted in the relatively large volume ballast chamber. Thus, there remains a need to provide an elemental analyzer which uses less oxygen, is faster, and is more sensitive, particularly when relatively small samples are being analyzed.